1. Field of the Invention
This invention relates to an (a first) electronic component such as a BGA (Ball Grid Array) chip or the like and a process for manufacturing the same, and more particularly to an (a first) electronic component wherein an electric contact as a contact terminal of the (first) electronic component is formed by subjecting to a surface treatment with an alloy containing tin and silver without the inclusion of lead causing an environmental problem and reduces a contact resistance as compared with an electric contact of an electronic component formed by a conventional surface treatment with an alloy containing tin and lead.
2. Description of Related Art
A conventional electronic component, for example, a BGA chip provided on its undersurface with electric contacts as a grid pattern, each of which being made of a solder in a substantially semispherical shape, is detachably mounted onto a socket connector, whereby the electric contact(s) of the BGA chip is contacted with the respective contact(s) formed on a conductor of a substrate constituting the socket connector to attain an electric conduction.
The conventional BGA chip is constituted with a soft resin substrate or the like connected with a rigid ceramic through a rewiring layer, and an eutectic solder having a composition of 62 mass % Sn-38 mass % Pb or a solder having a composition of 85 mass % Sn-15 mass % Pb is placed on plural lands formed on a one-side surface of the soft resin substrate and subjected to a reflow treatment to form electric contacts. In general, each of the electric contacts is contacted with each of plural contacts formed on the conductors of the substrate constituting the socket connector so as to attain the electric conduction.
However, the lead is a harmful heavy metal to human body. If a product containing the lead becomes useless and is disposed to an outdoor, Pb is eluted from the product into an aqueous solution such as acid rain or the like. Such an eluted lead tends to cause serious problems such as pollution of global environment, bad influence on a living thing and so on, so that it is unfavorable from the problem on the environment to use the electric contact subjected to a surface treatment with a Snxe2x80x94Pb based alloy containing lead (for example, Snxe2x80x94Pb solder).
And also, in view of the application of the electronic component, the BGA chip is required to be able to repeatedly attach to and detach from the socket connector, so that when the electric contact of the BGA chip is contacted with the contact of the socket connector by attaching the BGA chip to the socket connector, it is desirable to always obtain a stable value of contact resistance. However, when the BGA chip provided with the electric contacts formed by subjecting to the tin-lead surface treatment is repeatedly attached to and detached from the socket connector, the value of the contact resistance largely changes every attachment or detachment of the BGA and hence the stable value of the contact resistance can not be obtained.
To this end, it is demanded to develop electric contacts stably providing a contact resistance value and formed by subjecting to a surface treatment with a new composition system in place of the tin-lead solder containing lead.
It is, therefore, an object of the invention to provide an electronic component such as a BGA chip which is provided with electric contacts formed by subjecting to a surface treatment with an alloy containing tin and silver and containing no lead, which causes a problem on the environment, and stabilizes a contact resistance of the electric contact as compared with that of an electric contact of an electronic component formed by subjecting to the conventional surface treatment with the tin-lead alloy as well as a process for manufacturing the same.
According to a first aspect of the invention, there is the provision of an (a first) electronic component provided with an electric contact(s) producing an electric conduction by contacting with a contact of a second electronic component, said electric contact comprising a lead-free alloy layer containing tin and silver, a surface layer portion of said alloy layer at least contacted with the contact of the second electronic component being a tin-rich layer having a tin content higher than that of the other portion of the alloy layer.
In a preferable embodiment of the first aspect of the invention, the contact is formed on a conductor of a substrate constituting the second electronic component and the electric contact is formed on a conductor of a substrate constituting the first electronic component.
In another preferable embodiment of the first aspect of the invention, the first electronic component is a ball grid array (BGA) chip and the electric contact is formed on a conductor arranged at one side of a substrate constituting the BGA chip in a substantially semispherical shape by using an alloy solder containing tin and silver.
In the other preferable embodiment of the first aspect of the invention, a top of the electric contact in the BGA chip contacts with the contact of the second electronic component.
In a further preferable embodiment of the first aspect of the invention, the second electron component is a socket connector and the BGA chip is detachably mounted onto the socket connector to contact the contact of the socket connector with the electric contact of the BGA chip.
In a still further preferable embodiment of the first aspect of the invention, the alloy layer is a tin-silver-copper alloy layer containing no less than 90% of tin.
According to a second aspect of the invention, there is the provision of in a process for manufacturing an (a first) electronic component provided with an electric contact(s) producing electrical conduction by contacting with a contact(s) formed on a conductor of a substrate constituting a second electronic component, an improvement wherein a lead-free alloy layer containing tin and silver is formed on a conductor of a substrate constituting the first electronic component and subjected to a reflow treatment and then cooled at a relatively slow cooling rate to form the electric contact.
In a preferable embodiment of the second aspect of the invention, a surface layer portion of the alloy layer at least contacted with the contact of the second electronic component is provided with a tin-rich layer having a tin content higher than that of the other portion of the alloy layer.
In another preferable embodiment of the second aspect of the invention, the cooling after the reflow treatment is carried out at a cooling rate of no more than 50xc2x0 C./min.
In the other preferable embodiment of the second aspect of the invention, the first electronic component is a ball grid array (BGA) chip and the electric contact is formed on a conductor arranged at one side of a substrate constituting the BGA chip in a substantially semispherical shape by using an alloy solder containing tin and silver.
In a further preferable embodiment of the second aspect of the invention, the alloy layer is a tin-silver-copper alloy layer containing no less than 90% of tin.
In a still further preferable embodiment of the second aspect of the invention, the second electron component is a socket connector and the BGA chip is detachably mounted onto the socket connector to contact the contact of the socket connector with a top of the electric contact of the BGA chip.
According to the invention, as the electric contact of the (first) electronic component is formed by subjecting to the surface treatment with the alloy containing tin and silver without lead causing an environmental problem, there is not caused the environmental problem resulted from the outflow of the lead.
And also, the contact resistance in the electric contact of the (first) electronic component according to the invention can be largely reduced as compared with that of the electric contact in the conventional electronic component formed by subjecting to the surface treatment with the tin-lead alloy.
In the (first) electronic component according to the invention, even when the electric contact is repeatedly contacted with a contact of the second electronic component, the scattering of the contact resistance is small, and it is possible to always attain electric conduction at a low contact resistance.